The default is: [+] and [-]. Could not find a way to change it to other icon. For example down and right from https://ant.design/components/icon/.
My users are very very picky.
Thanks!
Found it:
.ant-table-row-expand-icon-cell {
position: relative;
.ant-table-row-collapsed:after {
content : "\E61D";
font-family: "anticon" !important;
font-style: normal;
vertical-align: baseline;
text-align: center;
text-transform: none;
text-rendering: auto;
right: 16px;
top: 0;
display: inline-block;
transform: scale(0.66666667) rotate(0deg);
transition: transform 0.3s cubic-bezier(0.645, 0.045, 0.355, 1);
zoom: 1;
}
.ant-table-row-expanded:after {
content : "\E61D";
font-family: "anticon" !important;
font-style: normal;
vertical-align: baseline;
text-align: center;
text-transform: none;
text-rendering: auto;
right: 16px;
top: 0;
display: inline-block;
transform: rotate(180deg) scale(0.75);
transition: transform 0.3s cubic-bezier(0.645, 0.045, 0.355, 1);
zoom: 1;
}